1. Field of the Invention
This invention relates to a combustion chamber of an internal-combustion engine and more specifically to a geometrical shape of a piston cavity of a combustion chamber.
2. Discussion of the Background
In the prior art combustion chamber of a diesel cycle engine, the quantity of noxious gas generated during the combustion process depends on the nature of the injected fuel and the geometrical shape of the combustion chamber wherein the injected fuel and the air are mixed and, more particularly, on the piston cavity shape of the combustion chamber. Piston cavities of combustion chambers have a variety of shapes such as a shallow dish shape, a toroidal shape, a reentrant shape, a Meurer shape, a spherical shape, a quadrangular shape etc. and variations of the above-noted shapes.
Deep piston cavities of combustion chambers have a tendency to emit a lot of hydrocarbon and nitrogen oxides and generate a lot of smoke when the engine is accelerated. Medium depth piston cavities of combustion chambers with various shapes are generally used for small and medium engines (refer to Japanese Patent Publication (B2) No. (Sho) 60-56893). Reentrant shape piston cavities are known as giving better mixation of fuel together with air by better squish air motion occurring at the end of compression by piston.
In order to get optimum combustion, the combustion chamber is so constructed that the injected fuels are primarily mixed with the air swirl generated and are burned in the combustion chamber, thereafter the smoke (polymer) resulting therefrom is reburned and also unburned hydrocarbon and carbon monoxides are reburned simultaneously with the proper quantity of remaining air. Also if the smoke, hydrocarbons and carbon monoxides are secondarily reburned and thus their quantities are remarkably reduced, then one can adjust the combustion procedure so as to reduce the generation of nitrogen oxide compounds. In order to inject the secondary air, another air injection valve may be mounted, but it cannot give satisfactory results. Since the time period of the combustion procedure is extremely short and the diffusion combustion during which the secondary air is needed is shorter than the above, and thus setting the injection time and adjusting quantity of the injection air in accordance with engine load, the injection quantity of fuel become very complicated to determine.
Therefore, it is most desirable that this be done in some manner in a combustion chamber in which air is not used for the initial combustion stage and is used for the diffusion combustion period. In actuality, such a device depends on the geometrical shape of the combustion chamber. Among the methods for arranging the device described above, given the recessed space in the bottom surface of a cavity, this cannot give satisfactory results since the fuel penetrates into and fills the space before combustion occurs. Usually the injection directions of the fuel are from the top of combustion chamber to the bottom of the cavity, even if it is somewhat with an inclination and the injection pressures is very high. However, if the recessed space is made perpendicular to the direction that the piston ascends and descends, and fuel is sprayed so as to hit the wall of the piston main cavity of the combustion chamber, the injected fuel forms circles, moves in a swirling action and burns so that the air in the space is not used for the initial combustion stage but rather is used for the diffusion combustion stage.
Therefore, a quadrangular shaped combustion chamber was made for a toroidal shaped piston cavity, however it has not only a drawback in that the required quantity of the secondary air cannot be optimized but also the force of eddy flow is not strong enough in utilizing the secondary air for attaining the required objectives, while the outlet of the space is dispersed as shown in FIG. 4-A (refer to Japanese Patent Publication (B2) No. (Sho) 60-24289).